Deacidification Treatments Of Printed Cellulosic Materials

ABSTRACT

A deacidification composition for use in for treating printed cellulosic materials is provided. A method of making the composition and a method of preparing components of the composition also are provided. The composition includes zinc oxide in the form of nanoparticles and/or nanoclusters.

CROSS-REFERENCE To RELATED APPLICATIONS

This application claims the benefit of Provisional Application Ser. No. 61/855,982, filed May 29, 2013, and Provisional Application Ser. No. 61/957,301, filed Jun. 29, 2013, which are incorporated by reference herein.

FIELD

The present application relates generally to compositions and methods for deacidification treatment and preservation of printed cellulosic materials, such as books, manuscripts and other image and information bearing documents and publications and works of art on paper, which may deteriorate or which may have become deteriorated through aging, insects, fungi and the like.

BACKGROUND

During the past 150 years, archives and libraries have struggled to prevent the aging of paper, i.e., yellowing and embrittlement of paper in documents and books. Many treatments to avoid or stop this aging have been proposed. The primary goals of these treatments are to either (1) transform the paper into another, more stable format or medium such as stable paper or microfilm, or electronic media such as cassette tapes, disks, (2) remote digital collections accessible through Google or the internet in remote computer organized collections, or (3) stabilize the paper against aging by deacidification. Deacidification has advantages in its effectiveness for many more years, continuing availability of original documents as stabilized materials for use, and lower unit treatment costs.

Although previously known treatments reduce the rate that books and documents are aging, known methods have the potential to deface or otherwise so harm significant portions of the collection so that the items are rendered unsatisfactory for ordinary use. Furthermore, numerous problems and environmental concerns exist with current treatment methods.

Moisture variation in anhydrous raw materials presents a significant problem when using some known treatment methods, particularly methods where the active ingredients are the magnesium single and double alkoxides solutions that become unusable by forming gels and/or precipitates, but are otherwise known to produce excellent deacidification in single sheet and mass preservation treatments.

There are a number of prior deacidification techniques and compositions. A first form uses soluble agents in water, such as in the form of carbonated aqueous solutions. The agents may include magnesium or calcium bicarbonate alkaline cations (HMgCO₃)⁺ that neutralize acids and buffer by depositing basic magnesium carbonate.

Another method uses soluble agents in solvents, which include flammable and nonflammable solutions. In these systems, agents such as Mg or Mg/Ti, carbon 1-3, and can include alkoxide molecules which are soluble in solvents to neutralize acids, and buffer by depositing basic magnesium carbonate and other similar material in paper. Active molecular agents for single metal alkoxides may include, for example, methoxy magnesium methyl carbonate or ethoxy magnesium ethyl carbonate. The active molecule for double alkoxides may include materials such as magnesium ethylate and titanium ethylate.

In yet another form, suspensions of bulk industrial particles may be used. In this form, typically agents may include magnesium oxide, calcium oxide and other metal oxide powders. The materials are typically in constantly agitated solvents that include surfactants, dispersants, or wetting agents to form poor suspensions that must be constantly stirred and tend to deposit defacing powders. Powders can be felt as powdery surface deposits and are visibly present on paper surfaces when treated.

However, prior deacidification technologies which (1) use particles larger than about 10 nm in diameter, (2) are suspended in anhydrous solvents or dry air during the particle impregnation treatment phase, and/or (3) are returned directly with no intervening treatment to normal or equivalent library collection storage, typically require a specially designed high relative humidity treatment to provide the moisture necessary for complete deacidification to occur.

Aqueous deacidification agents are standards against which other preservation treatments are measured. Wetting causes paper fibers to swell, paper to change dimensions and appearance, open pores to more penetration, change the documents' dimensions, strength, and flexibility, may destroy or change some inks and media, and cause more change than other treatments. Solutions are normally made in carbonated water at time of use from the metal carbonates, hydroxides, or oxides, and used as calcium, magnesium, and/or zinc carbonated cations having about 0.5 nm diameters.

In some of the prior techniques, as the quantity of moisture increases, either powder or gel precipitates will be formed, depending on time, reactivity, temperature and pressure conditions. These precipitates may prevent (poison), impede (slow) a manufacture or reaction rate and detrimentally affect the deacidification workability of solutions (clog spray nozzle assemblies, precipitate on paper surfaces and clog paper substrates). The precipitates also may deposit on and deface books and documents and block or clog filters, pipes, valves and other restricted passages in processing equipment. They may also deposit thick coatings on walls of tanks and, depending on relative densities, separate into top or bottom phase composition layers or even, in extreme cases, actually turn the treating solution (initially thinner than water) into an immobile gelatin-like gel.

Although produced, ultra-low moisture alcohol and aliphatic hydrocarbon and other solvents are not available commercially in standard containers, e.g., in 5-gallon pails or 55-gallon drums. Industrial solvent manufacturers do not deliver their solvents in an ultra-dry condition, i.e., below 15 or 25 ppm. For example, the minimum moisture content specification for a 55-gallon drum of research grade “anhydrous” methanol from Fisher Scientific is 500 or 1,000 ppm.

Sub-micron (less than 0.2 microns) coal black particles are known to precipitate in concentrates prepared for current treatment methods. The particles may be introduced as trace heavy metal (iron, cobalt, copper, etc.) impurities in the metals reacted with alcohols to produce alkoxide powders for use in treatment or by external conditions. These particles contaminate and discolor the treatment concentrate and must be removed before use in paper preservation. Additionally, allowing the particles to agglomerate naturally then filtering through a 0.1 micron absolute membrane filter limits the concentration of treatment concentrates that can be manufactured. For example, concentrations of organic magnesium of up to only 25 percent by weight in ethanol are a practical maximum.

The more alkaline pH values produced by organic magnesium carbonate treatments may cause undesirable color changes. These treatments may cause sensitive inks, pigments, and dyes to change color when the cellulosic material is changed from a deteriorating acidic condition to a stable alkaline condition.

The traditional chlorofluoro carbon (CFC) and hydrochlorofluorocarbon (HCFC) solvent systems for organic metal carbonate deacidification compositions tend to deface or damage some types of inks and/or cause structural book components to dissolve or soften. The more sensitive inks soften, bleed, strike through, offset, and in some cases, even glue the leaves of pamphlets and books together into solid blocks. In addition, the use of chlorofluorocarbon solvents is detrimental to the ozone layer and generally are prohibited by environmental regulations. Therefore, the use of such solvents should include recovery of the solvent to minimize release into the atmosphere.

A further deacidification method is used by the Library of Congress whereby diethyl zinc is used for treating the materials. However, this composition and process has a number of deficiencies. For example, the treatment occurs slowly at low vacuum pressures. Additionally, the method uses a hypergolic gas which can be violent, reacting very quickly and giving off extreme heat. In other words, the composition and method are susceptible to explosions and fires. Further, the speed at which the composition reacts with cellulose can cause the surface of the paper fibers to be coated instead of permitting the composition to penetrate and provide complete deacidification.

Deacidification for art, in many cases, is also similarly deficient. The Victoria and Albert Museum, London, developed the first nonaqueous deacidification treatment around 1895. It consisted of brushing barium hydroxide dissolved in methanol against the backs of paintings to neutralize and precipitate the soluble salts that acidic fumes from coal gas lights caused and were defacing Royal Images on paintings. Deacidification really began with the treatments that Otto Schierholtz invented, W. J. Barrow implemented into practice, and the U.S. National Archives applied on a mass basis in the late 1930s. Since then conservators and preservation scientists have gradually developed the three groups of truly excellent paper preservation treatments listed above. This patent application proposes to evaluate its zinc oxide nanocluster and nanoparticle treatments to clearly explain that zinc oxide by itself is capable of replacing the present uses of the three groups, and with assistance from additional metal oxide nanoparticles and petrochemical gases provide comprehensive deacidification and preservation treatments that will keep ordinary paper readable for 500 to 1,000 years.

Despite extensive efforts and the many solutions proposed for stopping aging, a truly satisfactory method that extends the useful life of cellulosic materials for hundreds of years has not been developed. No effective treatment is known that is acceptable and affordable for essentially all paper, inks, pigments, media, or other components of printed materials and is not hazardous to users.

Accordingly, there is a need to provide improved deacidification compositions and methods for making them, for preserving printed and written cellulosic materials, such as books, drawings, maps, works of art, manuscripts and images.

Additionally, there is a need to provide a method for universally preserving these cellulosic materials bearing printing, writing, drawings, or other recordings, with little or no impairment of inks, images, bindings or other visual or structural features.

SUMMARY

The compositions and methods described herein provide a one-time comprehensive paper treatment that protects paper and books against normal deterioration and/or wearing out. Heretofore, that objective or possibility was neither realistic nor possible. The deacidification compositions described herein are effective for treating and preserving printed cellulosic materials. Also described herein are methods treating and preserving printed cellulosic materials and methods of making the deacidification compositions including preparing components of these compositions.

These compositions and methods provide new and unexpected results as compared to previous processes, such as those described in U.S. Pat. No. 6,676,856 to Smith and U.S. Pat. No. 5,322,558 to Wittekind et al. which use alkoxides in separate processes. These unexpected results include extraordinarily fast preservation treatment times by the compositions described herein which may not precipitate or deposit on paper surfaces at least to the extent the deposits cannot be seen by the naked human eye with 20/20 vision under ambient lighting conditions. Indeed the compositions and methods described herein deacidify the cellulosic material or paper without requiring large amounts of time for removal of solvent reactants and permits deacidification without requiring exposure of the process to controlled high relative humidity.

In an important aspect, the deacidification composition comprises three principal components: (1) one or more active ingredients that significantly slow or stop the rate at which the cellulosic materials age or strengthen of otherwise rejuvenate the cellulosic materials, (2) one or more solvents (propellants) into which the active ingredients(s) are dispersed and impregnated throughout the cellulosic material, and (3) if needed, a surfactant, dispersant, and/or wetting agent which causes the active ingredients to separate into functional and stable materials.

The deacidification composition can be used to form a variety of stable materials. In one form, stabilized soluble ions or molecules under about one nanometer in diameter, or nanocluster particles from about 1 to 10 nm in diameter, or nanoparticles from about 10 to 200 nm in diameter can be used and/or formed. These materials can become ionic or molecular solutions in water condensed in capillary tubes of paper fibers and are capable of migrating throughout paper, paper substrates, and lumens inside paper fibers to thoroughly deacidify paper materials. They may also form as 1 to 10 nm nanoclusters form colloidal solutions in solvents and migrate through pores averaging 7.0 nm in diameter in walls of paper fibers to deacidify the paper, paper substrates, and lumens of paper fibers. They may also form colloidal solutions as nanoparticles 10 to 200 nm in diameter which thoroughly impregnate paper materials and substrates but not the 7 nm pores in walls of paper fibers or the lumens inside paper fibers.

The deacidification of paper materials impregnated with nanoparticles having 10 to 100 nm diameters occurs after solvent removal and drying in a subsequent high relative humidity—carbon dioxide, vapor phase process where water condensed in paper fiber capillary tubes reacts to form soluble (OMgCO3)+cations that migrate throughout the damp paper neutralizing acids and buffering paper. In one form, this vapor phase process can be greatly accelerated by wrapping (sealing) the books in nonpermeable film after water condensation, and creating a vacuum at about 10 psig so that a typical book is subjected to the equivalent of approximately 500 psi squeezing pressure for a period of about 5 to 7 days. If a stiffening sheet is inserted against the binding, the plastic wrapped or bagged, damp, vacuum-squeezed books, may be stored upright on library book shelves during the five to seven days required for self-deacidification.

In one form, treatment suspensions may be stable, water-clear or slightly hazy, colloidal solutions that will not leave visible, defacing deposits that can be seen or felt. According to one form, effective concentrations of zinc oxide range from about 0.1 to 3.0 wt. %. The concentration of zinc oxide is preferably from 0.25 to 1.0 wt. % and more preferably is 0.5 to 0.75 wt. %.

In one form, the components in the composition are provided in amounts which are effective to deacidify the cellulosic material to provide preservation of a paper substrate of at least 300 years according to at least one, but preferably both, of accelerated aging tests TAPPI T-453 and TAPPI T-544, without necessity of exposing the cellulosic material or paper to high moisture/humidity levels and without creating a precipitate visible to a naked human eye on the surface of the cellulosic material being treated with the deacidification composition.

In one form, the composition includes zinc oxide having a particle size of about 1 to about 10 nanometers such that the particles may be considered to be nanoclusters. In another form, the composition includes zinc oxide having a particle size of about 10 to about 100 nanometers.

In another aspect, one general method for preservation of acidic paper with nanocluster particles and nanoparticle zinc oxide deacidification composition begins with dispersing the zinc oxide nanoparticles plus their surfactant into a stable, water-clear, colloidal suspension suitable for application to books, documents, and works of art, as an aerosol spray, by brushing or dipping, or in chemical processing equipment, and removing the solvent by drying to thoroughly deacidify (neutralize acids and buffer against re-acidification in future. The treatment composition consists of zinc oxide in a concentration of about 0.1 to about 3 wt. % by weight, the zinc oxide particles having an average particle size diameter from about 3.0 nm to about 8.0 nm. In one form the particle size range is from about 1.0 nm to about 12.0 nm. The composition can be prepared in an ultrasonic mixer in a suitable solvent and containing sufficient surfactant, to produce a water-clear or slightly hazy colloidal solution.

In another form, larger zinc oxide particles with diameters from 10.0 nm to about 200.0 nm, and average diameters from 30.0 nm to about 80.0 nm, may be used with the same or similar solvents and ultrasonic solvent mixer plus a surfactant to form a clear or slightly hazy colloidal solution. When using the larger particle size, faster mixing, and less surfactant can be used. Further, the necessity for another deacidification treatment may be eliminated along with the elimination of solvent and liquid water usage in one mass treatment variation.

According to one form, suitable solvents may include water, aliphatic flammable solvents, such as pentane, hexane, and heptane, hexamethyldisiloxane, and propellants such as A70 (Isobutane/propane) and B70 (butane/propane); and nonflammable solvents such as 3M Novec EF 7100, & EF-5660 and HCFC-225 (dichloropentafluoropropane), and propellants such as HFC-134a and HFC-152a. One liter of zinc oxide was prepared using a one liter plastic beaker and mixed on an Hielsuper Ultrasonic UP200Ht. pH values following treatment ranged from 7.0 to 7.5.

The components of the composition may include suitable alkaline particles and/or ions and molecules that are small enough to enter the pores of most paper fibers and cellulose materials. The average size of pores through walls of paper fibers in conventionally dried cellulose materials is typically less than about 7 nm. In some forms, the active materials in the present compositions may have sizes in a range of about 0.5 to about 10 nanometers. In this regard, the active materials are small enough to enter the pores of the cellulose materials. In another form, the active materials in the compositions have sizes in a range of about 10 to about 100 nanometers. In this form, the treatment includes exposure to over 70% relative humidity air containing carbon dioxide that causes moisture condensation in paper fibers to form soluble alkaline carbonate cations. Further, in some forms, the active materials have a combined solubility that an effective amount of the active materials remains in the pores and throughout the lumens of the fibers of the cellulose materials as the solvent is removed.

DETAILED DESCRIPTION

The present application is directed to a composition and method for treating printed cellulosic materials to preserve the materials with little to no negative impact on inks, images, bindings or other features. The application also is directed to methods of making the composition. More particularly, the application is directed to compositions including metal agents such as zinc oxide. The metal agents may be combined with a variety of other components and may be administered in a number of different treatment methods and systems. In one form, zinc oxide may be combined with a flammable or nonflammable aliphatic hydrocarbon solvent such as Phillips 66 ULACH Heptane or 3M Novec Engineering Fluid 7100 plus a surfactant, wetting or dispersing agent, and a propellant such as DuPont HFC-134a or Distributor's A or B 70 and then administered as an aerosol deacidification spray. When the propellant is excluded, the solution can be applied by bushing or immersing etc. The compositions can be used in sprays and solutions to protect books and documents against aging. It should be understood that a variety of other materials, such as metal oxides may be used as will be understood from the below discussion.

Deacidification solutions as described herein may be used to introduce one or more active materials into the cellulose/paper fiber while solvents can be removed, thereby leaving behind an effective amount of active materials to deacidify the cellulose. Further, solvent removal can cause some of the active materials to move about in the paper fibers, thereby helping to ensure that the active materials reach far more of the cellulose fibers than occurs by simply wetting. Moreover, while the compositions are described as deacidifying the cellulose materials, it should be noted that at least in some cases little to no moisture is used or even needed in the process and/or solutions for absolutely thorough treatment to occur. Therefore, the active materials may interact or otherwise deacidify the cellulose even without the incorporation of much, if any, moisture for deacidifying, catalyzing and/or pH adjusting purposes. In other forms, moisture may be used with different particles and/or particle size to modify the particles and assist their alkaline component migration through the cellulose fibers. The moisture content may also be modified depending on the type of processing treatment, as will be explained below in more detail.

Zinc and/or zinc oxide is known to inhibit and stop biological infestations, can assist in catalyzing condensation of petrochemical gases, strengthen cellulose, and prevent harmful effects of ultraviolet radiation. Other transient metals, such as magnesium, calcium, titanium, and hafnium or zirconium may also be used for deacidifying, catalyzing and/or pH adjusting purposes.

According to one form, a deacidification composition may be prepared using a variety of components. In one form, the composition includes a combination of at least one active ingredient that slows the rate at which cellulosic materials age, at least one solvent and, optionally, at least one surfactant. In one form, the at least one active ingredient includes zinc oxide.

Even more importantly, the nearly ideal benefits and properties of zinc oxide deacidification treatments may give conservators the capability to (1) develop comprehensive treatments that stop fungi and insects from attacking paper, (2) cause gases to both stabilize chemically active residues (inside paper fibers that papermaking must leave), and (3) strengthen weak aged papers sufficiently for scholarly study and use indefinitely.

It should be understood that the zinc oxide particles may take a variety of forms and particle sizes. In one form, the zinc oxide is in the form of nanoparticles and/or nanoclusters. For example, the particles may range from about 1 nanometer to about 200 nanometers. Different sized particles may be used in different compositions and used in different methods. In one form, the zinc oxide particles are in a range of about 1 nanometer to about 10 nanometers. In a preferred form, the zinc oxide particles are about 5 nanometers ±2 nanometers. In another form, the zinc oxide particles range from about 10 nanometers to about 100 nanometers. Larger particles may not be used in the same manner as the smaller particles but may provide other benefits such as: larger particles cost less, smaller quantities of expensive surfactant are needed for their effective dispersal, and the carbonate cations formed when ZnO is dissolved in the water condensed from RH inside paper fibers are very small. Small particles, such as 0.5 nm diameter, are highly mobile, and are thoroughly dispersed and impregnated by solvent flow and chemical equilibrium forces throughout paper substrates and inside paper fiber walls and lumens.

As mentioned above, particles having a particle size of about 1 nanometer to about 10 nanometers may be used and may be suitable for entering the pores of cellulose materials conventionally dried in a papermaking machine or process. Larger zinc oxide particles from 10 nm to 100 nm may not be suitable for this type of application to neutralize and buffer the bound acids in papermaking residues deposited inside paper fibers to provide a significant degree of protection against aging.

In one form, zinc oxide particles from about 10 to 200 nm are generally not visible to the naked eye, do not deposit defacing residues on surfaces of paper fibers, and are too big to penetrate the average size air-dry pores in the walls of conventionally dried paper fibers. It is believed that the average diameter of pores in conventionally dried paper fibers lies in a range around 7 nm, probably not larger than 10 nm. The diameter has a narrow range because of the chemical structure of cellulose. Paper fibers shrink more in diameter than in length and tend to develop a roughly rectangular shape. Zinc oxide particles that are about 10 to about 200 nm may be dispersed and impregnated such as by being suspended in a nonaqueous solvent or suspended-in-air by sonic vibration as taught in U.S. Pat. No. 6,214,165 to Kundrot.

Other larger particles include bulk-sized-industrial alkaline powders (particles typically average 1.0 microns (+2 microns, −700 nm)). These particles can be intentionally impregnated (a) during papermaking in the paper-machine's head-box into an acidic fiber paper-furnish, or (b) as the active agent in a preservation deacidification treatment. However, the normal size range of these alkaline particles (for example, magnesium oxide are much too big to penetrate through the 7 nm pores of conventionally dried paper fibers and neutralize the bound-acid residues deposited inside paper fibers during papermaking by acidic pulping or acid sizing processes or acidic gasses and particles absorbed from air pollutants since manufacture.

In one form, the average diameter of particle sizes was about 5 nm with a distribution range from 3 to 7 nm when optically measured with a ZEM Microscope using a 20 nm grating plate. The Surface Area Test Results for one gram of the 5 nm +/−2 nm particles have a surface area of 41.7 sq. meter per gram. This size and specification were selected because particles close to 100% effective are obtained and the quantities used may be minimized. It is obvious to those knowledgeable that production treatment scale experience will provide data for specifying still effective and less costly raw materials.

Other materials in the composition, such as surfactants, wetting agents and dispersants, etc. may be used to adjust or modify the solubility and compatibility of nanoclusters and nanoparticles in water, flammable and nonflammable solvents to fit with the service conditions and properties of materials being preserved. However, preservation treatments mostly use solvents as carriers of choice for nanoparticles because “deacidification and preservation” aims to improve and maintain the original appearance, availability, and handling properties of books, documents and works of art without causing visible changes. Conservators choose solvents that have minimal effects on the components of these objects, do not leave residues that may cause problems in future, and are safe to handle both for themselves, their customers, and the objects. In addition, access to large portions of paper, “the insides of paper fibers,” are extremely difficult to reach because the (1) 7 nm pores in paper fiber walls block access and (2) the small size and large surface area of nanoclusters require more surfactant which reduces its dispersing capability and damage nanoproperties.

The compositions may include one or more of a variety of surfactants, dispersants, and wetting agents. The fact zinc oxide is hydrophilic and hydrophobic indicates each solvent group: water, flammable hydrocarbon solvent like heptane, and nonflammable hydrocarbon solvent like Novec EF 7100 may need a different surfactant. When preserving paper, a material sensitive to acids, it may be important to reject an excellent surfactant to avoid acid attack. Suitable surfactants may include DuPont Capstone surfactants FS-3100 and FS-83 which are useful for dispersing zinc oxides in hydrofluorochlorocarbon solvents such as HFC-134a. Dow Chemical Triton HW-1000 particularly and TergitolTMN-H6 (90%) may also be used. HW-1000 provides high wetting capability and low equilibrium and dynamic surface tensions for zinc oxide in heptane, Golden MF-310 and Fluorolink F10 warrant consideration with 3M Novec EF 7100 if an acidic material is allowable.

The composition may also include other metal oxides in combination with zinc oxide. In this form, metals oxides such as calcium, magnesium, titanium, cerium and hafnium oxide may be used. These materials may also provide other benefits to the composition. For example, titanium may protect against ultraviolet radiation while other oxides may provide catalytic capabilities.

The treatment composition may also include ultra dry solvents. The commercially available solvents that may be used in the present invention include alcohols having 1 to 4 carbon atoms and aliphatic and halogenated hydrocarbon solvents. Such solvents include methanol, ethanol, isopropanol, isobutanol, propane, butanes, pentanes, isohexanes, heptanes, difluoroethane (HFC-152a), and tetrafluoroethane (HFC-134a), HFC-32, HFE 7100, HFE 7200, and HFC-10 43MEE.

In one aspect, the composition comprises fluorocarbon solvents. Preferably, the fluorocarbon solvent is HFC-134a. Mass deacidification solutions containing HFC-134a solvent have almost no detrimental effect on all printing inks tested. Higher alkaline reserves are possible, if desired, because the nanoparticle metal oxides form stable colloidal just like organic carbonates, such as methoxy magnesium methyl carbonate (MMMC) concentrates, have high solubility in HFC-134a. It is possible to achieve increased concentrate solubility using fluorocarbon solvents in the composition of the present application, as well as hydrocarbon solvents as compared to chlorofluorocarbon solvents.

Previously soluble inks, such as purple mimeograph, photocopy, and fast printing, offset inks that HCFC solvents such as HCFC-22 destroyed, are unaffected by treatment with HFC-134a or HFC-152a. Other detrimental effects are eliminated because no co-solvent alcohols are required with metal oxides.

An almost total lack of ink solubility (when HFC-134a solvent is substituted) indicates that alcohols have not caused inks to feather, offset, or run, etc., as heretofore believed. (Rather the CFC and HCFC solvents most likely caused such results.) As a result, low unit cost universal mass deacidification treatment is possible for preservation of archive and library general collections. The pre-selecting or exclusion of collections or individual books for suitability for deacidification, e.g., ink sensitivity, physical condition, or type of paper, may not be necessary.

Solvents in the mass deacidification composition can be completely recovered and recycled indefinitely with minimal benefaction requirements beyond adjustment for additional alcohol introduced in the make up concentrate.

Further, it should be noted that a number of different solvents are identified herein. Such solvents include hydrocarbon, hydrofluorocarbon, hydrochlorofluoro carbon, amongst others. It should be noted that where one of these solvents is identified, any of the solvents may be used, unless specifically indicated otherwise. Further, examples of other solvents include, but are not limited to, dichloropentanefluoropentane, amongst other solvents.

One method for general preservation of acidic paper with a nanocluster zinc oxide particle deacidification composition requires mixing zinc oxide from a minimum of 0.1% to a maximum level of 3% by weight with an average particle size diameter from about 3.0 nm to about 8.0 nm, having a diameter size range from about 1.0 nm to about 12.0 nm, in an ultrasonic mixer in a suitable solvent and containing sufficient surfactant, until a water-clear or slightly hazy colloidal solution is produced. Suitable solvents are water, aliphatic flammable solvents, such as pentane, hexane, and heptane, hexamethyldisiloxane, and propellants such as A70 (Isobutane/propane) and B70 (butane/propane); and nonflammable solvents such as 3M Novec EF 7100, & EF-5660 and HCFC-225 (dichloropentafluoropropane), and propellants such as HFC-134a and HFC-152a.

Another method for general preservation of acidic paper with a nanoparticle zinc oxide particle deacidification composition is similar to preparing nanocluster composition. The major differences are particle sizes increase, mixing time and quantity of surfactant lower, a second deacidification treatment is necessary, but wetting and solvents may be eliminated. The composition requires mixing zinc oxide from a minimum of 0.1% to a maximum level of 3% by weight with an average particle size diameter from about 10.0 nm to about 200.0 nm, having a diameter size range from about 30.0 nm to about 80.0 nm, in an ultrasonic mixer in a suitable solvent and containing sufficient surfactant, until a water-clear or slightly hazy colloidal solution is produced. Suitable solvents are water, aliphatic flammable solvents, such as pentane, hexane, and heptane, hexamethyldisiloxane, and propellants such as A70 (Isobutane/propane) and B70 (butane/propane); and nonflammable solvents such as 3M Novec EF 7100, & EF-5660 and HCFC-225 (dichloropentafluoropropane), and propellants such as HFC-134a and HFC-152a.

For example, the unstable acidic paper in a work of art was deacidified with an aqueous aerosol can using the following composition described herein. A 1.0% concentration of ZnO (5 nm +/5.0 -2.0 nm nanoclusters) was mixed using a Hielsuper Ultrasonic UP200Ht into a water-clear colloidal aqueous suspension deacidification composition. The composition was poured into a pint size aerosol spray can and sprayed onto the verso of a slightly damp work of art placed face down on a suitable support and then sprayed thoroughly damp with the aqueous deacidification spray and covered with a clean and also sprayed damp rag mat. The treatment was applied twice over a 24-hour period. Following drying under pressure, the work of art was carefully examined. No visible color staining, deposits, or other changes of appearance were found and the paper tested as having a pH or 7.3 to 7.5 on front and back using a Contact pH Meter.

According to one form, zinc oxide particles in a range of about 10 to about 10 nanometers may be used in a simple process. Most of these particles are small enough such that they are highly likely to enter through the 7 nm pores in paper fibers and thoroughly deacidify the bound-acids locked inside paper fibers. In one form, no special subsequent treatments are required beyond insuring that the paper materials undergoing treatment remain thoroughly wetted with the zinc oxide long enough for the effects of Brownian and meniscus movements inside paper fibers to continue for a long enough time period (5 to 10 minutes) to insure deacidification and buffering.

In one form, the composition can be used in a freezer-type application. In this form, the process uses 85 to 95% relative humidity with carbon dioxide atmospheres at cool temperatures 35 to 55° F. to condense water inside capillary tubes. Vacuum wrapping the damp books in Saran (or other nonporous to air, H₂O, or CO₂ vapor) plastic shrink film at about 2 to 6 psi causes in situ formation of zinc oxide carbonated cations (0.5 nm average diameter and their migration throughout the book inside paper fiber water-filled capillary tubes). In one form, full deacidification (neutralizing and buffering against re-acidification) may take about one week while the vacuum-squeezed, shrink-wrapped books sit on library bookshelves. The carbon dioxide prevents fungus attack and fumigates the book during this period. This treatment occurs without the presence of liquid water, a major advantage. Following deacidification completion, the books are frozen, film wrapper removed, and vacuum-freeze-dried. Following re-humidification to about 40 to 45% relative humidity, the now thoroughly stabilized alkaline paper books may be returned to library collections for patron use.

In yet another form, a solvent process may be used. In this form, zinc oxide may be suspended in solvents preferably aliphatic solvents like heptane, liquefied refrigerant gases like HFC-134a, etc. or gases like air and nitrogen and subsequently converted into alkaline cations that migrate in the water in capillary tubes of paper fibers to penetrate paper fibers and cause deacidification. Similar cations and benefits may also be obtained using and in situ reaction where the alkaline powders were impregnated using larger industrial bulk powders.

The compositions described herein may be used in existing treatment processes as a replacement composition and/or a supplemental composition. For example, the zinc oxide compositions may be used in:

Bookkeeper Treatment, Preservation Technologies, Glendale, Pa., U.S. Pat. No. 4,522,843 to Kundrot, and subsequent patents (Solvent suspended MgO particles, average diameter 1.0 μm, +2.0 μm, −0.7 μm);

Paper Save Swiss, Nitrochemie Wimmus, Switzerland, Double metal alkoxides, U.S. Pat. No. 5,322,558 to Wittekind et al., and U.S. Pat. No. 6,676,856 to Smith; and

PaperGuard, Wei T'o Associates, Matteson, Ill., single metal alkoxides, U.S. Pat. No. 3,676,182 to Smith, U.S. Pat. No. 3,939,091 to Kelly, and U.S. Pat. No. 6,676,856 to Smith, and other patents.

In an important aspect, the compositions described herein can be used as a drop-in replacement in other deacidification processes. For example, the composition can be used with HFC-134a as a deacidification solvent as invented by Smith in U.S. Pat. No. 5,322,558 (2003) and applied at Wei T'o Canada through 2005. At that time, Wei T'o prepared its concentrates by dissolving ethoxy magnesium ethyl carbonate into ethanol, and mixed that concentrate into HFC-134a. For this drop-in replacement test, the concentrate for dilution into HFC-134a is prepared by using the ultrasonic UP200Ht In-Line mixer to continuously mix the ZnO (5.0 +/−2.0) powder into Phillips 66 ULACH Heptane and then stir-blending that concentrate into the HFC-134a. Following preparation of the liquefied gas deacidification solution, a set of air-dry books were loaded into Wei T'o's mass Deacidification System and the process conducted normally with exceptions that the books no longer required drying, heptane was substituted for methanol, and zinc oxide nanoclusters for MMMC. The treatment results were as expected, deacidified paper had pH values ranging from 7.3 to 7.5 and there were no new deposits of defacing powder, or transferred or blotted ink or other defacing from the zinc oxide nanocluster deacidification treatment.

In mass treatment forms, as well as other forms, thorough drying under vacuum of the materials to be treated is no longer an absolute requirement. Normally air dry books and documents as received from the library collections can be deacidified as received in preservation. The materials then are contacted with the composition for a period of time effective for thoroughly wetting the materials. During contact, the composition may be impregnated under pressure into the materials. After the solution is removed from the materials, any solution remaining in the materials is vaporized for recovery and recycling to vacuum conditions. In some forms of this process, it is possible to recover at least about 95-98% of the deacidification solution, which can be re used in the process.

Further, the present application is directed to a method, including a plurality of sub processes and systems, which may be used separately and/or in combination to deacidify and/or otherwise preserve cellulosic materials. For example, in one form, such treatment may include: (1) vacuum drying the material to be treated to 50 mtorr; (2) immersing the material to be treated in a liquefied gas solvent-deacidification solution; (3) removing the solution and solvent to deposit agents and alkaline reserve throughout the material to be treated and fibers; (4) solvent recovery and recycling in a vacuum and/or air conditioning phases; (5) catalyzing petrochemical gas free radical monomers into stabilizing cellulose and strengthening the material to be treated; and (6) reconditioning the deacidified, stabilized, strengthened and sterilized materials.

Moreover, in one form, ambient humidification can be used. Therefore, no special high humidity processing steps are required. However, it should be noted that high humidity processing steps can be included if desired. In another form, ambient humidity conditions, such as during storage, may be sufficient to rehydrate the treated cellulose.

In one form, the process is environmentally sustainable, emits no contaminates, and deposits only stable, safe residues. Although preparation of deacidification concentrate solutions may occur in separate locations from the deacidification treatment site, the capture, recycling, and preparation of virgin quality recyclable solutions may preferably occur on the treatment site.

The foregoing descriptions are not intended to represent the only compositions and use of the compositions. The percentages provided herein are by weight unless stated otherwise. Changes in form and in proportion of parts, as well as the substitution of equivalents, are contemplated as circumstances may suggest or render expedient. Similarly, while exemplary compositions and methods have been described herein in conjunction with specific embodiments, many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. 

What is claimed is:
 1. A deacidification composition comprising: zinc oxide, the zinc oxide being present in the form of nanoparticles and/or nanoclusters and having a particle size in a range of about 1 to about 200 nanometers, the zinc oxide being present in an effective amount to slow the rate at which cellulosic material ages; a solvent; and a surfactant.
 2. The deacidification composition of claim 1 wherein the zinc oxide has a particle size in a range of about 1 to about 10 nanometers.
 3. The deacidification composition of claim 1 wherein the zinc oxide has a particle size in a range of about 10 to about 100 nanometers.
 4. The deacidification composition of claim 1 further comprising at least one additional metal oxide besides zinc oxide.
 5. The deacidification composition of claim 1 further comprising a nonaqueous solvent.
 6. The deacidification composition of claim 1 further comprising an aqueous solvent.
 7. The deacidification composition of claim 1 wherein the zinc oxide is present in an amount of about 0.1 to about 3 wt. %.
 8. The deacidification composition of claim 7 wherein the zinc oxide is present in an amount of about 0.5 to about 0.75 wt. %.
 9. The deacidification composition of claim 1 wherein the surfactant is selected from the group consisting of fluorosurfactants, branch secondary alcohol ethoxylates, non-ionic hydrocarbons, perfluoropolyethers and the like.
 10. A method for preserving cellulosic material, the method comprising: providing a cellulosic material; and exposing the cellulosic material to a deacidification composition, wherein the deacidification composition comprises zinc oxide and a solvent, the zinc oxide being present in the form of nanoparticles and/or nanoclusters and having a particle size in a range of about 1 to about 200 nanometers, the zinc oxide being present in an effective amount to slow the rate at which cellulosic material ages.
 11. The method of claim 10 wherein the step of exposing the cellulosic material to a deacidification composition includes a step selected from the group consisting of applying the deacidification composition as an aerosol to the cellulosic material, brushing the deacidification composition on the cellulosic material, and immersing the cellulosic material in the deacidification composition.
 12. The method of claim 10 wherein the zinc oxide is provided in the deacidification composition in an amount of about 0.1 to about 3 wt. %.
 13. The method of claim 10 wherein the solvent is an aqueous solvent.
 14. The method of claim 10 wherein the solvent is a nonaqueous solvent.
 15. The method of claim 10 wherein the zinc oxide has a particle size in a range of about 1 to about 10 nanometers.
 16. A method for preserving cellulosic material, the method comprising: providing a cellulosic material; exposing the cellulosic material to a deacidification composition; exposing the cellulosic material to conditions having at least about 70% relative humidity to form a humidified cellulosic material; and freeze drying the humidified cellulosic material to remove moisture, wherein the deacidification composition comprises zinc oxide and a solvent, the zinc oxide being present in the form of nanoparticles and/or nanoclusters and having a particle size in a range of about 1 to about 200 nanometers, the zinc oxide being present in an effective amount to slow the rate at which cellulosic material ages.
 17. The method of claim 16 further comprising exposing the cellulosic material to carbon dioxide to form carbonate cations in the cellulosic material.
 18. The method of claim 16 wherein the cellulosic materials are exposed to at least about 70% relative humidity at a temperature of less than about 60° F.
 19. The method of claim 16 wherein the zinc oxide includes particles having a diameter in a range of about 10 to about 200 nanometers.
 20. The method of claim 16 wherein the zinc oxide is provided in the deacidification composition in an amount of about 0.1 to about 3 wt. %. 